The CDF - GMV will definitely be booked HST though.
I don't see how you could reach that conclusion. Have I missed something? I note that all the Cardiff shunts are based on their WTT timings, reflecting the timing loads (HSTs) that match the usual Cardiff to Taunton allocations, but all the stabling locations reflect the usual Great Malvern / Gloucester to Westbury / Weymouth service, as will the crew diagrams north of Bristol Parkway, so it is presumably a mix of 158s and 16x.
My best guess at the diagrams for 2 August - 7 August is the following. Arguably 2 could be a HST (as the usual 0655 Gloucester to Penzance is a HST) but it seems to couple with 4 for the 1242 Gloucester to Cardiff Central. These all look like units to me.
1
5G77 0425 Gloucester Carriage Sdgs to Gloucester
2G77 0437 Gloucester to Worcester Shrub Hill
2T63 0520 Worcester Shrub Hill to Cardiff Central
5C67 0725 Cardiff Central to Cardiff Central
2E54 0800 Cardiff Central to Great Malvern
5O98 1030 Great Malvern to Great Malvern
2T98 1041 Great Malvern to Cardiff Central
5C79 1330 Cardiff Central to Cardiff Central
2E66 1401 Cardiff Central to Great Malvern
5C28 1631 Great Malvern to Great Malvern
2T28 1644 Great Malvern to Cardiff Central
5C91 1930 Cardiff Central to Cardiff Central
2E78 2000 Cardiff Central to Worcester Shrub Hill
2T40 2237 Worcester Shrub Hill to Bristol Temple Meads
5M95 0050 Bristol Temple Meads to St Philips Mrsh H S T D
2
5C65 0536 St Philips Mrsh H S T D to Gloucester
2T65 0655 Gloucester to Cardiff Central
2E56 0900 Cardiff Central to Gloucester
5E56 1038 Gloucester to Gloucester Carriage Sdgs
5C18 1152 Gloucester Carriage Sdgs to Gloucester
2T18 1242 Gloucester to Cardiff Central
5C81 1430 Cardiff Central to Cardiff Central
2E68 1500 Cardiff Central to Gloucester
2T82 1641 Gloucester to Cardiff Central
5C89 1825 Cardiff Central to Cardiff Central
2E76 1900 Cardiff Central to Gloucester
2T34 2041 Gloucester to Cardiff Central
5U32 2224 Cardiff Central to St Philips Mrsh H S T D
3
5G79 0550 Gloucester Carriage Sdgs to Gloucester
2G79 0604 Gloucester to Worcester Shrub Hill
2T72 0707 Worcester Shrub Hill to Cardiff Central
5C71 0927 Cardiff Central to Cardiff Central
2E58 1000 Cardiff Central to Great Malvern
5T78 1230 Great Malvern to Great Malvern
2T78 1242 Great Malvern to Cardiff Central
5C83 1530 Cardiff Central to Cardiff Central
2E70 1600 Cardiff Central to Worcester Foregate Street
5T32 1825 Worcester Foregate Street to Worcester Foregate Street
2T32 1853 Worcester Foregate Street to Cardiff Central
5C95 2131 Cardiff Central to Cardiff Central
2E82 2200 Cardiff Central to Gloucester
5E82 2348 Gloucester to Gloucester Carriage Sdgs
4
5Y06 0553 Gloucester Carriage Sdgs to Cheltenham Spa
2T06 0614 Cheltenham Spa to Bristol Parkway
2E52 0754 Bristol Parkway to Gloucester
2T74 0842 Gloucester to Cardiff Central
5C73 1029 Cardiff Central to Cardiff Central
2E60 1100 Cardiff Central to Gloucester
2T18 1242 Gloucester to Cardiff Central
5C81 1430 Cardiff Central to Cardiff Central
2E68 1500 Cardiff Central to Gloucester
2T82 1641 Gloucester to Cardiff Central
5C89 1825 Cardiff Central to Cardiff Central
2E76 1900 Cardiff Central to Gloucester
2T34 2041 Gloucester to Cardiff Central
5U32 2224 Cardiff Central to St Philips Mrsh H S T D
5
5O01 0511 Westbury Dmu Sidings to Westbury
2O01 0524 Westbury to Salisbury
5G81 0556 Salisbury to Salisbury
2G81 0634 Salisbury to Cheltenham Spa (via Swindon)
5G81 0907 Cheltenham Spa to Gloucester Carriage Sdgs
5O76 1031 Gloucester Carriage Sdgs to Gloucester
2T76 1041 Gloucester to Cardiff Central
5C77 1226 Cardiff Central to Cardiff Central
2E64 1300 Cardiff Central to Gloucester
2T22 1440 Gloucester to Cardiff Central
5C85 1627 Cardiff Central to Cardiff Central
2E72 1700 Cardiff Central to Gloucester
2T30 1842 Gloucester to Cardiff Central
5C93 2028 Cardiff Central to Cardiff Central
2E80 2100 Cardiff Central to Gloucester
5E80 2241 Gloucester to Gloucester Carriage Sdgs
6
5F03 0510 St Philips Mrsh H S T D to Bristol Temple Meads
2E50 0555 Bristol Temple Meads to Worcester Foregate Street
5C12 0758 Worcester Foregate Street to Worcester Foregate Street
2T12 0855 Worcester Foregate Street to Cardiff Central
5C75 1130 Cardiff Central to Cardiff Central
2E94 1200 Cardiff Central to Great Malvern
5O80 1431 Great Malvern to Great Malvern
2T80 1441 Great Malvern to Cardiff Central
5C87 1727 Cardiff Central to Cardiff Central
2E74 1800 Cardiff Central to Great Malvern
5T36 2042 Great Malvern to Great Malvern
2T36 2116 Great Malvern to Cardiff Central
5U34 2342 Cardiff Central to St Philips Mrsh H S T D